A wide variety of electric incandescent lamps employ a coiled refractory metal filament as the light source means to provide general illumination. Recent development of increasingly more energy efficient as well as more optically precise light sources require the coiled filament to be accurately centered within the lamp envelope. More particularly, one such energy efficient lamp employs an elongated tubular lamp envelope with the coiled filament being aligned substantially coincident with the longitudinal axis of the lamp envelope and provides a reflective film on the lamp envelope to reflect infrared radiation back to the lamp filament. A representative structural configuration for such type lamp is disclosed in U.S. Pat. No. 4,588,923, assigned to the assignee of the present invention and which is specifically incorporated herein by reference into the present application since the same general lamp configuration can be employed in one embodiment of the present lamp improvement. Still other optical considerations dictate precise centering of the coiled filament within the lamp envelope when such light source is lodged within a related lighting device such as a reflector lamp as recognized in the previously cited commonly assigned Ser. No. 06/944,918 application now abandoned. Manufacturing constraints hinder these efforts since the conventional coiled filaments are produced by winding a single strand of the refractory metal wire on a retractable or dissolvable mandrel. This manufacturing technique restricts the filament geometry and dimensions to relatively simple configurations such as cylindrical or rectangular shapes. Additionally, the central portion of such filaments cannot be larger in diameter than the coil end turn diameter.
Coiled refractory metal filaments having improved physical configurations to provide a more precise light source means in an electric incandescent lamp are thereby still highly desirable. To further illustrate, coiled filaments formed in exterior shape of an ellipse or hyperboloid would enable such light source means to avoid several optical drawbacks now encountered with the conventional cylindrically shaped coil filaments in reflector lamps. Such provision of a point type illumination source in a reflector lamp further enhances focusing of the overall output light beam pattern. Accordingly, such improvement would not only find utilization in reflector lamps suitable for more precise indoor illumination but would prove equally beneficial in other type end-product applications such as vehicle headlamps, flashlights, and the like. It becomes further desirable in such manner to provide a coiled filament having an external contour which more closely adheres to the interior shape of the lamp envelope. Better conformity in this regard can reduce the end losses now experienced in the aforementioned prior art lamps which utilize a reflective film in conjunction with a cylindrical coil lodged in the lamp envelope having a tubular envelope shape. Still other coiled filament shapes prove desirable based upon related optical considerations for an electric incandescent lamp. Adjusting the lighted portion of the coiled filament along its length again enhances centering of the light source within the lamp envelope. Moreover, it becomes further desirable that the length of the lighted portion of the coiled filament be accurately and easily adjusted so as to provide various operating wattage ratings for an incandescent lamp.
It is a principal object of the present invention, therefore, to provide improved light source means for an electric incandescent lamp utilizing a coiled refractory metal filament which has various novel physical configurations.
It is another important object of the present invention to provide improved means whereby such novel coiled refractory metal lamp filaments are centered within the envelope member of an electric incandescent lamp.
A still further important object of the invention is to provide electric incandescent lamp constructions exhibiting improved operating efficiency attributable to novel light source means therein being employed.
Still a further important object of the invention is to provide an improved coiled filament assembly for an electric incandescent lamp enabling still more reliable lamp manufacture, particularly with existing high speed lamp manufacturing equipment.
These and other objects of the present invention will become more apparent upon consideration of the following description for the present invention.